88 STUDIES IN GENERAL PHYSIOLOGY 
strange object’’ drives the moths into the flame. We find, 
however, that the caterpillars of Porthesia chrysorrhea 
creep as well toward the sun as toward a lamp. Yet, 
according to Romanes, the sun ought to be a familiar ob- 
ject to these animals. Such anthropomorphic opinions as 
those of Romanes are evidently as useless in the analysis 
of life-phenomena as the speculations of metaphysicians — 
e. g., Hegel’s— on physical phenomena. A scientific analysis 
of the behavior of moths toward light leads to a very simple 
explanation of the paradox. 
Experiment 1.—Specimens of Sphinx euphorbie, Bom- 
byx lanestris, and other moths are kept in a large glass box. 
The box is placed in a room into which only daylight and no 
artificial light enters. As soon as the animals begin to 
fly, at the approach of twilight or later, they collect at the 
window side of their boxes. Whenever the box is reversed 
the animals fly back to the window side. This experiment 
is rendered more complete by the following observations: 
I kept the pupz of moths in an open box. Most of 
the moths hatched at night. On the following morning I 
always found them collected at the closed window of the 
room. Here they remained all day exposed to the light. 
Finally, when I caused the moths to fly by day, I noticed 
that they flew to the window as do all other positively 
heliotropic insects. These experiments show that the 
animals are attracted, not only by a lamp, but also by 
diffuse daylight. They also show that Réaumur’s idea that 
moths shun daylight is wrong. The experiments indicate 
that the animals are positively heliotropic toward diffuse 
daylight, although, as we shall soon see, this positive helio- 
tropism may during the daytime be obscured by another 
form of irritability. 
Experiment 2.—I brought some specimens of Sphinx 
euphorbie into a room which had a window only on one 
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